Liquid crystal displays (LCDs) are widely utilized in various electronic products, such as electronic watches, calculators or the like. In order to provide a wide viewing angle, Fujitsu Corp proposed a technique of Multi-domain Vertical Alignment (MVA) in 1997. The technique of MVA not only can provide a view angle of 160°, but also can achieve a high contrast ratio and fast response. However, the technique of MVA has a remarkable disadvantage, i.e. a phenomenon of color shift occurs in the case of wide viewing angle. For example, the color of human skin will be shown inaccurately, especially the color of Asian skin.
FIG. 1 schematically shows a diagram of the relationship between voltages applied to a pixel and transmittances of liquid crystal molecules in an LCD employing the technique of MVA, where the horizontal axis represents the voltages in units of Volts applied to the pixel, and the vertical axis represents the transmittances of liquid crystal molecules. When human eyes look at an LCD employing the technique of MVA straightly, the variation of transmittance with the applied voltages is indicated by the curve 101; when human eyes look at the LCD obliquely, the variation of transmittance with the applied voltages is indicated by the curve 102. As shown in FIG. 1, there exists a deviation in the curve 102 compared with the curve 101. In the region 100 of the curve 102, the transmittance of liquid crystal molecules is not quickly increased with the increase of the applied voltages just like the case of human eyes straightly looking at the LCD, the increase speed thereof is obviously reduced and thereby an ideal transmittance cannot be reached. Such a phenomenon is the main reason that causes the color shift.
Conventionally, a method for solving the above problem is to form two sub-pixels in a pixel which may have different relationship curves of the transmittance and the applied voltages so as to compensate the deviation of the relationship curve of the applied voltage and the transmittance in the case of oblique viewing. As illustrated in FIG. 2, the curve 201 is the relationship curve of the transmittance and the applied voltages corresponding to a first sub-pixel in the pixel, while the curve 202 is the relationship curve of the transmittance and the applied voltages corresponding to a second sub-pixel in the same pixel. As shown by the curve 203 in FIG. 2, the better relationship curve of the transmittance and the applied voltages can be achieved by the superposition of the two curves 201 and 202, i.e. by the superposition of the optic characteristics of the two sub-pixels.
As a result, how to produce at least two sub-pixels in one pixel and make the individual sub-pixels applied with different pixel voltages under a same drive signal becomes the object to be sought. Based on this object, a plurality of pixel structures for compensating color shift have been proposed. FIG. 3 shows two pixel structures including two sub-pixels in the prior art, wherein by appropriately designing capacitance parameters of the two sub-pixels during the manufacturing of the LCD (for example, designing different values of Ccp or adjusting the values of storage capacitor Cst of the two sub-pixels), the two sub-pixels may have different voltages when displaying, and thereby the phenomenon of color shift can be compensated by superposition of the optic characteristics of the two sub-pixels.
Although the color shift can be compensated to some extent by using the pixel structures shown in FIG. 3, the disadvantage of these structures is that it is almost impossible for the capacitance parameters to be modified after the designing and manufacturing of an LCD. Because of the disadvantage, the application of such types of LCDs is not flexible enough. Moreover, during the application of these LCDs, the capacitance parameters thereof may be slightly changed and as a result, the expected compensation effect for color shift cannot be achieved. Therefore, it is desirable to design such an LCD structure that the voltage difference between sub-pixels in the pixel structure can be easily adjusted without changing structural parameters of the LCD and thus the compensation effect for color shift can be adjusted.
A liquid crystal display is disclosed in the patent publication No. CN 101004502A, in which the adjustment to the voltage difference between sub-pixels in the pixel structure is realized by providing a number of voltage supplies for applying common voltages to pixel units. The pixel structure of the LCD is shown in FIG. 4. In such an LCD, the voltage difference between sub-pixels is generated by coupling common electrodes of different sub-pixels to voltage supplies having different voltages, and the voltage difference between the sub-pixels can be changed by adjusting the voltage waveforms supplied by those voltage supplies. Although it is achieved that the voltage difference between the sub-pixels in the pixel structure being adjusted by such an LCD, the provided voltage supplies are too many and the pixel structure is too complex.